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From "Aaron Whiteside (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (CASSANDRA-9328) WriteTimeoutException thrown when LWT concurrency > 1, despite the query duration taking MUCH less than cas_contention_timeout_in_ms
Date Mon, 26 Oct 2015 18:48:27 GMT

    [ https://issues.apache.org/jira/browse/CASSANDRA-9328?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14974817#comment-14974817
] 

Aaron Whiteside commented on CASSANDRA-9328:
--------------------------------------------

If this is a known issue, and there is no other ticket to represent this issue, then please
tell me again why you want to close it? This ticket should remain OPEN until the issue is
resolved, regardless of the fact there is no known solution.

And I don't see any documentation on this feature that says it will provide non-deterministic
behavior under light (2 threads) contention. 

I disagree on your point that you can read the value after writing it to determine if the
LWT was successful. You forget in a concurrent environment that this is the very definition
of a race condition. With the current LWT implementation you can NEVER know 100% if an update
succeeded or not. If you think this is not true please provide sample code on how to accomplish
this.. if such a thing exists it should also be added to the official documentation as a work
around on how to use LWT "correctly".


> WriteTimeoutException thrown when LWT concurrency > 1, despite the query duration
taking MUCH less than cas_contention_timeout_in_ms
> ------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: CASSANDRA-9328
>                 URL: https://issues.apache.org/jira/browse/CASSANDRA-9328
>             Project: Cassandra
>          Issue Type: Bug
>          Components: Core
>            Reporter: Aaron Whiteside
>            Priority: Critical
>             Fix For: 2.1.x
>
>         Attachments: CassandraLWTTest.java, CassandraLWTTest2.java
>
>
> WriteTimeoutException thrown when LWT concurrency > 1, despite the query duration
taking MUCH less than cas_contention_timeout_in_ms.
> Unit test attached, run against a 3 node cluster running 2.1.5.
> If you reduce the threadCount to 1, you never see a WriteTimeoutException. If the WTE
is due to not being able to communicate with other nodes, why does the concurrency >1 cause
inter-node communication to fail?



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